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A study of  MADAGASCAR AMETHYST
 
( SiO2 )   Faceted Amethyst click here !
(Variety of Quartz)                Bi scepter amethyst crystal, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data
· Crystallographic properties:
Trigonal System (Subdivision of the hexagonal system)
Crystal structure of amethyst :
Quartz forms hexagonal prisms at the blunted ends and the head 
finishing in hexagonal pyramids.
· Physical properties
Hardness 7 
Density 2.65 - 2.66 
Refractive Index: 1.54 -1.55 + 0.009 positive uniaxial 
Glare:  vitreous
· Chemical Composition:
Silicium Dioxide   ( SiO2 )
The colouring of amethysts is due to the presence of colour centers which come from substitution of ions of
silicon by iron ions in the crystal lattice of quartz.
For example, the amethyst crystallizes at lower temperatures than smoky quartz.In Madagascar, we find it either in
 crypts of pegmatites, or in quartzite veins in connection with those.
The geodes of the siliceous nodules of basalts contain some too.
The first have an hexagonal network, although their pattern of crystallization is only of ternary order.  The seconds 
have a ternary network.  The elementary mesh is a rhomboedron, i.e. a parallelepiped consisted six equal 
rhombuses.  
A ternary axis A3 joint the tops of the regular trihedrons, three normal binary axes A2  with the ternary axis joining 
the meddle of opposite horizontal corners.
Here elements of  symmetry of the Trigonal system with 
the oblique shape, the tetragonal scalenoedron.
          
It is interesting to see what  becomes this tetragonal scalenoedron in others classes where the disappearance of 
the symmetry planes makes decrease of half the number of the faces. We obtain a trapezohedron (One notices that 
these two trapezohedrons are not superposable. It is said that they are two enantiomorphism shapes. They are 
symmetrical compared to a symmetry plane.)

One speaks about right trapezohedron and left trapezohedron (just as we have a right hand and a left hand, 

nonsuperposable thus enantiomorphism).

Certain minerals present sometimes left forms sometimes right forms.  The most known example is that of quartz.  
The distinction between left quartz and right quartz has a certain importance in the electronics industry where one 
uses the piezo-electric properties of this mineral.
The negative crystals of hexagonal shape can contain liquids like water, gas, as well as rutile needles, tiny hematite
discs, goetite, fushsite or mica.

                                             

Inclusions of H2O and CO2 in an amethyst from Madagascar. Habitus type of flattened Dauphiné.
   
 

 

This marvellous Bi-terminated amethyst of 128 grams also contains water drops in its center.  Habitus type of rhomboedron.

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The amethyst scepters are also typical in Madagascar.
  
Here, a scepter in the blackberry shape.
There, the stem of the scepter developed by crystallizing around it a quantity of small points in hedgehog. Length:40 mm.

                           

   
Double scepter.

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Double scepter amethyst crystal, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data amethyst crystal scepter, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data
Head of amethyst scepter crystal, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data Head of scepter: 132 grams

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Amethyst in castle on its quartz gangue.  986 grams.

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Cluster amethyst crystal, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data
The fact that sometimes a thin surface layer of violet color be only presents in the stone or that this color is not 
homogeneous, makes often a difficult cutting.  The art of lapidary is to place the color correctly in order to make
homogeneous the tone of cut stones.  The distribution of the color in a cut stone is observed simply by 
immersing it in water contained in a transparent container and colourless. The color of amethyst varies from purple 
reddish to purple bluish while passing by straightforwardly crimsons tone.  Thus of very variable intensity, the color 
is often laid out in stripes parallel to the final faces of the crystal.
Rough amethyst crystal, violet Madagascar quartz, exclusive amethysts minerals, amethyste information data  

 

 

Faceted amethyst, violet Madagascar gemstone, exclusive cut amethysts, amethyste information data   Enlarge

 ¦ Cutting Styles ¦ Characteristics ¦ Crystalline Systems ¦
¦ Amethyst Crystal 1 ¦ Amethyst Crystal 2 ¦ Amethyst Scepter ¦ Faceted Amethyst ¦
   
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© All of the pictures on this website have been shot by gggems.com Alain Darbellay
     Text written by Alain Darbellay.
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